linux-kernel - Re: [PATCH v2 1/7] s390/kdump: implement is_kdump

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Message-ID: <87sespfwtt.fsf@li-0ccc18cc-2c67-11b2-a85c-a193851e4c5d.ibm.com>
Date: Mon, 21 Oct 2024 14:46:06 +0200
From: Alexander Egorenkov <egorenar@...ux.ibm.com>
To: David Hildenbrand <david@...hat.com>
Cc: agordeev@...ux.ibm.com, akpm@...ux-foundation.org,
        borntraeger@...ux.ibm.com, cohuck@...hat.com, corbet@....net,
        eperezma@...hat.com, frankja@...ux.ibm.com, gor@...ux.ibm.com,
        hca@...ux.ibm.com, imbrenda@...ux.ibm.com, jasowang@...hat.com,
        kvm@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-s390@...r.kernel.org, mcasquer@...hat.com, mst@...hat.com,
        svens@...ux.ibm.com, thuth@...hat.com, virtualization@...ts.linux.dev,
        xuanzhuo@...ux.alibaba.com, zaslonko@...ux.ibm.com
Subject: Re: [PATCH v2 1/7] s390/kdump: implement is_kdump_kernel()

Hi David,

David Hildenbrand <david@...hat.com> writes:

> Makes sense, so it boils down to either
>
> bool is_kdump_kernel(void)
> {
>           return oldmem_data.start;
> }
>
> Which means is_kdump_kernel() can be "false" even though /proc/vmcore is 
> available or
>
> bool is_kdump_kernel(void)
> {
>           return dump_available();
> }
>
> Which means is_kdump_kernel() can never be "false" if /proc/vmcore is 
> available. There is the chance of is_kdump_kernel() being "true" if 
> "elfcorehdr_alloc()" fails with -ENODEV.

Do you consider is_kdump_kernel() returning "true" in case of zfcpdump or
nvme/eckd+ldipl dump (also called NGDump) okay ? Because
dump_available() would return "true" in such cases too.
If yes then please explain why, i might have missed a previous
explanation from you.

I'm afraid everyone will make wrong assumptions while reading the name
of is_kdump_kernel() and assuming that it only applies to kdump or
kdump-alike dumps (like stand-alone kdump), and, therefore, introduce
bugs because the name of the function conveys the wrong idea to code
readers. I consider dump_available() as a superset of is_kdump_kernel()
and, therefore, to me they are not equivalent.

I have the feeling you consider is_kdump_kernel() equivalent to
"/proc/vmcore" being present and not really saying anything about
whether kdump is active ?

Regards
Alex